Following is a summary of the Pre-cleaning and Passivation (Pre-filming) processes and why they are important.
Prior to start-up of a new Cooling Tower pretreatment service, it is strongly recommended that the equipment be pre-treated in order to maximize the useful life of the system. Pre-treatment should include the following two components:
- Pre-cleaning, to remove dirt, debris, and residual manufacturing materials and/or scrap.
- Passivation/Pre-filming, to create a barrier against corrosion.
Pre-cleaning is necessary to ensure that the Pre-film and/or corrosion inhibitors will adhere sufficiently to the equipment. If the system is not precleaned, there will likely be an increase in the amount of corrosion during initial start-up. This will in-turn result in higher energy costs due to reduced heat transfer. Over time there will be higher maintenance costs and ulimately equipment failure.
The best time to do pre-cleaning is just before the scheduled start-up. pre-cleaning should then be followed immediately by Pre-filming, in the form of passivation. The pre-cleaning phase will typically require 10 to 24 hours. Pre-cleaning is complete after a heavy blow-down of the system to remove all of the cleaning chemicals and foreign material.
Pre-cleaning for most Cooling Towers will consist of a re-circulating flow of detergent, surfactant, and anti-foam through the heat exchange components. An effective pre-cleaning should remove any hydrophobic materials that are left behind from manufacturing, as well as light amounts of rust. During pre-cleaning it is important to ensure that the pH is kept between 5.5-7.0. For quicker results, elevated water temperatures (> 150 F) will likely produce faster and more effective removal of contaminates.
Immediately following pre-cleaning, the Passivation (aka pre-filming) should begin. Passivation is a common form of Pre-filming that provides a barrier to corrosion. The key to successful and enduring Pre-film is ensuring the the “film” created evenly and at the appropriate rate. Too slow and corrosion may begin before the layer is complete; Too fast and the film may have weak spots.
Pre-filming does not eliminate the need for ongoing water treatment, but it does provide a strong foundation from which to build a regular water treatment program. With ongoing treatment, on top of a well applied pre-film, the Cooling Tower will require less energy to operate and much less maintenance to keep it running. The system will also provide for more years of useful service.
Things to Remember:
Significant changes in environment (e.g., severe pH depression) can destroy the prefilm, and corrosion products can accumulate before the film is reestablished through normal treatment. When this occurs, a prefilming program may be necessary for rapid repassivation of the system. Pre-filming for Cooling Towers is also recommended following any deep chemical cleaning, or after significant changes in the environment, such as a sharp drop in pH.
Another method of prefilming is an increase in inhibitor levels for 6-24 hr. Although this is somewhat easier, it is less efficient and is generally used only when the continuous inhibitor program is phosphate-based.
In general, Pre-treatment and Passivation, followed by ongoing treatment programs, minimizes corrosion over the life of any heat transfer system. Less corrosion translates to lower operating costs due to the improved heat transfer, longer service life, and reduced maintenance requirements.
Aqua Clear offers pre-cleaning and passivation/pre-filming chemicals and services for new and existing Cooling Towers. We have been performing this service for over 10 years and we have the experience to ensure that the job is done right the first time.
If you are interested in learning more, or if you would like to schedule a site survey (no charge or obligation), please give us a call or send an e-mail. We look forward to hearing from you.